1. Field of the Invention
This invention relates, for example, to a surface acoustic wave device used for oscillators, filters, resonators, and the like.
2. Description of Related Art
In electronic equipment using high-frequency waves such as portable telephones and wireless communicators, surface acoustic wave devices are widely used for filters, resonators, oscillators, and the like, inside such electronic equipment.
This is a inter digital transducer-type electrode installed on a piezoelectric substrate such as quartz.
Conventionally, randomly-oriented polycrystalline aluminum has been used as this electrode.
However, in a surface acoustic wave device where such an electrode is used, oscillation frequency varies along with its use, preventing it from obtaining a constant frequency stably over a long period.
In order to overcome such a shortcoming, disclosed is the use of aluminum alloy as the electrode, although the orientation is random (Pat Pub Sho 61-47010).
However, even in such an electrode, when a surface acoustic wave device is used for a long period, the oscillation frequency changes over time, making it difficult to use a surface acoustic wave device stably over a long period.
The objective of this invention is to provide a surface acoustic wave device with an oscillation frequency that is hard to change over time.
The exemplary embodiments of the methods and systems of this invention to solve the above problems are as follows:
(1) A surface acoustic wave device that has a substrate made of piezoelectric material, and an electrode installed on the substrate and oscillates by conduction to the electrode, the electrode may consist of polycrystalline aluminum layer whose crystal boundaries are twin boundaries.
(2) The surface acoustic wave device described in above, where the piezoelectric material is quartz.
(3) The surface acoustic wave device described above, where the substrate is an ST-cut substrate of a rotational Y plate obtained by rotating a quartz Y plate by 10xc2x0 to 60xc2x0 around the X axis.
(4) The surface acoustic wave device described above, where the {1 1 1} plane of the aluminum is oriented to be inclined by 1xc2x0 to 30xc2x0 relative to the {0 1 0} plane of the said piezoelectric material.
(5) The surface acoustic wave device described above, where the (xe2x88x921 1 xe2x88x921) plane and the (1 xe2x88x921 1) plane of the aluminum are twin boundaries.
(6) The surface acoustic wave device described above, where the crystal grain of the (xe2x88x921 1 1) plane and the (0 0 2) plane of the aluminum and the crystal grain of the (1 xe2x88x921xe2x88x921) plane and the (0 0xe2x88x922) plane are in a twin crystal relationship.
(7) The surface acoustic wave device described above, where the thickness of the layer is 0.05 xcexcm to 20 xcexcm.
(8) The surface acoustic wave device described above, where the oscillation frequency is 10 MHz to 5000 MHz.
(9) The surface acoustic wave device described above, where the frequency change after 1000 hours of use is 50 ppm or smaller.
(10) The surface acoustic wave device described above, which has a reflector that strengthens the vibration.
(11) The surface acoustic wave device described above, where the reflector is made of the same kind of material as the electrode.